6V6 as rectifier in Eico 625 Tube Tester

[twilightofthedogs]

Picked up an old Eico 625 tube tester over the weekend. Seems to work and but I am planning on tidying it up a bit. I cracked it open to find, to my surprise, a 6V6 with a little trimmer pot added where a 6H6 is supposed to be. My understanding is that this is a rectifier. Is this crazy, or did some pre-internet guru rig this up in a workable manner with parts they had available? Since 6H6 are cheap and vintage 6V6 are nice in guitar amps I plan on putting it back to stock. Just curious about the theory.

[g1]

I don't see any rectification at all. Only cap is .005uF. Schematic on pg.11 of attached.

[Helmholtz]

Thanks for schematic.

V1 (6H6) is the rectifier, both diodes wired in parallel.

[g1]

So rectifier is in use only for one position of selector switch?
And 6V6 is functional as diode?

[J M Fahey]

Any tube is functional as a diode (Fets and transistors too) if needed.
Anyway I find it weird and would love to see what that switch position does/means.
Too sleepy now to analyze the circuit, be my guest.

Guess current involved is very low anyway,1mA tops.

OR they measure gain, transconductance, something "Audio" , and rectify amplified signal , then display it in the meter.

Or MAYBE it´s a voltmeter, I see they adjust primary voltage with a rheostat.

[twilightofthedogs]

Any tube is functional as a diode (Fets and transistors too) if needed.
Anyway I find it weird and would love to see what that switch position does/means.
Too sleepy now to analyze the circuit, be my guest.

Guess current involved is very low anyway,1mA tops.

OR they measure gain, transconductance, something "Audio" , and rectify amplified signal , then display it in the meter.

Or MAYBE it´s a voltmeter, I see they adjust primary voltage with a rheostat.

Fascinating. Thanks! According to a page on the 625 on DIY Audio Projects:

The lone 6H6 diode is used to rectify one of the AC filament voltage for the neon indicator bulb used for identify "Tube Short".